1. Field of the Invention
The present invention relates to method of producing hydrofluorocarbons, and particularly lower alkyl hydrofluorocarbons, from hydrochlorocarbons.
2. Description of Related Art
It is known that when certain halocarbons are released into the atmosphere, they undergo reactions that result in the depletion of the Earth's ozone layer. Examples of environmentally harmful halocarbons include certain hydrochlorocarbons (HCCs), hydrochlorofluorocarbons (HCFCs), and chlorofluorocarbons (CFCs). One such CFC is trichlorofluoromethane (CFC-11), a compound that conventionally has been used in foam insulation applications. Due to CFC-11's potential for environmental damage, replacements for this compound have been sought. One proposed substitute for CFC-11 in foaming application is 1,1-dichloro-1-fluoroethane (HCFC-141b). Although HCFC-141b also adversely affects the ozone layer, its impact is significantly less than that of CFC-11.
Certain lower alkyl hydrofluorocarbons, including the compound 1,1,1,3,3-pentafluoropropane (HFC-245fa), have been identified as a potential replacements for HCFC-141b in a variety of applications, most notably insulation and refrigeration applications. HFC-245fa has good insulation characteristics, low toxicity, correct vapor pressure and low flammability properties. Accordingly the demand for HFC-245fa has grown and as well as a need for more economical means of producing compounds such as HFC-245fa.
Methods for producing hydrofluorocarbons (HFCs) by reacting hydrogen fluoride (HF) with various hydrochlorocarbon and/or hydrochlorofluorocarbon compounds are known. For example, various schemes for producing HFC-245fa from 1,1,1,3,3-pentachloropropane (HCC-240fa) or 1,3,3,3-tetrachloro-1-propene (HCC-1230) and hydrogen fluoride (HF) either in the liquid or vapor phase have been described. See, for example, U.S. Pat. Nos. 5,902,912 and 5,710,352. For liquid phase processes, a catalyst such as SbCl5 or SbF3Cl2 is usually required to promote the exchange of chlorine atoms on the organic reactant with fluorine atoms of the hydrogen fluoride reactant. Unfortunately, the reaction conditions (e.g. reactant and catalyst concentrations, temperatures, pressures and the need for oxidants such as chlorine to maintain catalyst activity) required to promote this halogen exchange process can be extremely corrosive to metals commonly used for liquid phase reactors, such as Monel, Inconel and Hastelloy C. As a result of the extremely corrosive reaction environment most reactors used for fluorination processes must be lined with fluoropolymers. However, these lined reactors suffer from poor heat transfer and HF permeation of the liner. In addition, the use of Cl2 as an oxidant results in a yield loss due to chlorination of various raw materials, intermediates, and reactants.